Fuel consumption and exhaust emissions regulations on automobiles and other vehicles are becoming more and more stringent in these years and the future trend is toward even more stringent regulations. There is growing interest particularly in fuel consumption because of such issues as escalating gasoline prices, effect on global warming, and depletion of energy resources.
Under these circumstances, various technological developments are underway in many countries of the world for the improved vehicle fuel consumption. Examples of the technologies that have been developed include electric power drive represented by hybrid and electric vehicles and improved efficiency of the internal combustion engine represented by improved compression ratios, more accurately controlled fuel injection amount, and external EGR.
In terms of EGR, aims of introducing the EGR are to reduce work performed outside the system by a piston (pump loss) by reducing intake pipe vacuum (a difference between cylinder pressure during an intake stroke and atmospheric pressure) under a condition in which an output from the internal combustion engine is small and to reduce exhaust loss by controlling abnormal combustion (detonation) under a condition in which the output from the internal combustion engine is relatively large. Thus, due to a mounting need for improved fuel economy from vehicles, a need exists for a greater amount of EGR introduced to the intake pipe.
PTL 1 discloses an exemplary method for estimating an EGR amount (rate) to be recirculated from the exhaust pipe to the intake pipe.
With the more accurately controlled fuel injection amount, a purge system is known for controlling the internal combustion engine, in which activated carbon in a canister adsorbs fuel evaporative emissions and the emissions are diluted with atmosphere before flowing into the intake pipe, so that constant pressure can be maintained in the fuel tank. The purging allows the fuel evaporative emissions contained in purge gas to be introduced into the combustion chamber. Thus, reducing the fuel injection amount using the fuel injection valve is necessary to prevent the air-fuel ratio from being deviated. PTL 2 discloses an exemplary method for estimating a purge air-fuel ratio.